The typical aerospace electronic chassis box generally consists of multiple plug-in circuit cards which plug into and are interconnected by a “motherboard”. This motherboard must then be connected to the “outside world,” in order to provide communication from the plug-in circuit boards to external electronics and vice versa, by either a wire harness or a flex cable harness. The harness is then connected to connectors, which are generally cylindrical and are mounted in the wall or walls of the electronic chassis box in a well known manner. (See U.S. Pat. No. 5,093,759 for a discussion of these types of prior art systems, which is hereby incorporated in its entirety by reference.)
The plug-in circuit cards typically rely on some type of chassis card guides formed within the electronic box structure to align the cards with a receptacle connector on the motherboard and to physically support them as well. Providing accurate alignment of the cards to the motherboards and simultaneously physically supporting the cards requires tight dimensioning and tolerances, sometimes accurately pinning the motherboard within the chassis. The card guides must be located accurately and yet must provide some card displacement in order to allow the cards to plug into the receptacle connectors on the motherboard. The necessary card displacement results in a compromise situation wherein the card guides are less effective in supporting the cards during shock and vibration as well as being less effective in providing heat sinking from the cards to the chassis than could otherwise be achieved with a solid mounting of the circuit cards.
In some arrangements, the circuit cards, which are mounted in individual card edge guides formed in the outer walls of the electronic box, are inserted into respective receptacle connectors in the motherboard, the latter of which may be positioned between the circuit cards and the bottom of the electronic box. Interposing the motherboard between the circuit cards and the bottom of the box results in limited heat transfer from the electronics because the only heat transfer occurs from the edges of the cards across the side wall of the box. It is generally desirable to transfer heat through a larger surface area, not just from the edges of the cards.
As previously mentioned, the method of connecting to the outside of the electronic chassis box is usually accomplished by a harness connected from the motherboard to external connectors situated in the wall of the chassis. In a digital application the harness may consist of hundreds of wires. Where a wire harness is impractical, a flex cable is sometimes used. However, the flex cable must either be made part of the motherboard (called a “rigid-flex”), or made to plug into the motherboard with another pair of connectors. This latter technique has generally proven costly and difficult to implement.
Another prior art system, in an attempt to minimize the amount of space within the box occupied by an interconnecting harness cable, utilizes an arrangement of in-line connectors. The in-line connectors are mounted adjacent to a motherboard with the in-line connectors interconnected with connectors mounted to the motherboard. Circuit card edge guides are still required for retaining circuit cards connected to the mother board.
The use of plug-in circuit cards creates other limitations in addition to those mentioned above. In most aerospace applications, and especially spacecraft electronics, plug-in cards create limitations on the thermal and vibration environments which cannot be exceeded if the cards are to survive.
Accordingly, in view of the above, it is desirable to overcome the problems and limitations of the prior art by reducing and preferably eliminating the need for motherboard and circuit card guides for the support and interconnection of circuit cards in an electronic chassis box.